All living organisms take in food to gain energy for growth and survival. There are four main types of nutrition: autotrophic nutrition where organisms produce their own food through photosynthesis; heterotrophic nutrition where organisms rely on other organisms for food; saprotrophic nutrition where organisms obtain nutrients from dead and decaying matter; and parasitic nutrition where an organism lives on or inside a host organism and derives its nutrients directly from the host. Photosynthesis is the process by which plants and some other organisms convert light energy, water and carbon dioxide into oxygen and organic compounds like glucose to obtain chemical energy.